On 09/26/2013 09:26 AM, Mischa Jonker wrote:
Vipin wrote:
I have also faced this problem before. May be a better solution is to place all the struct and buffer declarations at the very start of dw_eth_dev structure (off-course with a comment that these should not be moved). It may avoid the problem in later modifications
I think that's why Alexey added the alignment to the struct dmamacdescr declaration, to make sure that it always aligned on a boundary of 16 bytes (so even 128-bit busses don't face this issue).
I don't know though whether the __aligned attribute should be at the type definition of the struct or at the declaration of the "struct dmamacdescr" inside "struct dw_eth_dev". I'm guessing the declaration inside "struct dw_eth_dev" will inherit the alignment requirements of the type def though, but not sure.
At least from what I see during my trials "__aligned" in definition of BD structure works as well. Both arrays of buffer descriptors were properly aligned compared to "dw_eth_dev" base address. And since "dw_eth_dev" structure is already aligned (it is allocated with "memalign") both BD arrays are also properly aligned.
Initially I thought about move of BD arrays on top of the mother structure but then decided to go with "__aligned" specifiers. IMHO it is safe enough while still very clear - no need to worry about order of structure members and no need to add any comments on how to keep members in order.
-Alexey